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/*
* Copyright 2011-2012 Branimir Karadzic. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without modification,
* are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice, this
* list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY COPYRIGHT HOLDER ``AS IS'' AND ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
* SHALL COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
* WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
* OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
* THE POSSIBILITY OF SUCH DAMAGE.
*/
package lz4
import (
"encoding/binary"
"errors"
)
const (
minMatch = 4
hashLog = 17
hashTableSize = 1 << hashLog
hashShift = (minMatch * 8) - hashLog
incompressible uint32 = 128
uninitHash = 0x88888888
// MaxInputSize is the largest buffer than can be compressed in a single block
MaxInputSize = 0x7E000000
)
var (
// ErrTooLarge indicates the input buffer was too large
ErrTooLarge = errors.New("input too large")
)
type encoder struct {
src []byte
dst []byte
hashTable []uint32
pos uint32
anchor uint32
dpos uint32
}
// CompressBound returns the maximum length of a lz4 block, given it's uncompressed length
func CompressBound(isize int) int {
if isize > MaxInputSize {
return 0
}
return isize + ((isize) / 255) + 16 + 4
}
func (e *encoder) writeLiterals(length, mlLen, pos uint32) {
ln := length
var code byte
if ln > runMask-1 {
code = runMask
} else {
code = byte(ln)
}
if mlLen > mlMask-1 {
e.dst[e.dpos] = (code << mlBits) + byte(mlMask)
} else {
e.dst[e.dpos] = (code << mlBits) + byte(mlLen)
}
e.dpos++
if code == runMask {
ln -= runMask
for ; ln > 254; ln -= 255 {
e.dst[e.dpos] = 255
e.dpos++
}
e.dst[e.dpos] = byte(ln)
e.dpos++
}
for ii := uint32(0); ii < length; ii++ {
e.dst[e.dpos+ii] = e.src[pos+ii]
}
e.dpos += length
}
// Encode returns the encoded form of src. The returned array may be a
// sub-slice of dst if it was large enough to hold the entire output.
func Encode(dst, src []byte) ([]byte, error) {
if len(src) >= MaxInputSize {
return nil, ErrTooLarge
}
if n := CompressBound(len(src)); len(dst) < n {
dst = make([]byte, n)
}
e := encoder{src: src, dst: dst, hashTable: make([]uint32, hashTableSize)}
binary.LittleEndian.PutUint32(dst, uint32(len(src)))
e.dpos = 4
var (
step uint32 = 1
limit = incompressible
)
for {
if int(e.pos)+12 >= len(e.src) {
e.writeLiterals(uint32(len(e.src))-e.anchor, 0, e.anchor)
return e.dst[:e.dpos], nil
}
sequence := uint32(e.src[e.pos+3])<<24 | uint32(e.src[e.pos+2])<<16 | uint32(e.src[e.pos+1])<<8 | uint32(e.src[e.pos+0])
hash := (sequence * 2654435761) >> hashShift
ref := e.hashTable[hash] + uninitHash
e.hashTable[hash] = e.pos - uninitHash
if ((e.pos-ref)>>16) != 0 || uint32(e.src[ref+3])<<24|uint32(e.src[ref+2])<<16|uint32(e.src[ref+1])<<8|uint32(e.src[ref+0]) != sequence {
if e.pos-e.anchor > limit {
limit <<= 1
step += 1 + (step >> 2)
}
e.pos += step
continue
}
if step > 1 {
e.hashTable[hash] = ref - uninitHash
e.pos -= step - 1
step = 1
continue
}
limit = incompressible
ln := e.pos - e.anchor
back := e.pos - ref
anchor := e.anchor
e.pos += minMatch
ref += minMatch
e.anchor = e.pos
for int(e.pos) < len(e.src)-5 && e.src[e.pos] == e.src[ref] {
e.pos++
ref++
}
mlLen := e.pos - e.anchor
e.writeLiterals(ln, mlLen, anchor)
e.dst[e.dpos] = uint8(back)
e.dst[e.dpos+1] = uint8(back >> 8)
e.dpos += 2
if mlLen > mlMask-1 {
mlLen -= mlMask
for mlLen > 254 {
mlLen -= 255
e.dst[e.dpos] = 255
e.dpos++
}
e.dst[e.dpos] = byte(mlLen)
e.dpos++
}
e.anchor = e.pos
}
}
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